The Seventh House is the western horizon of the chart, the point where the self meets the other. It is the house of partnership, marriage, and all one-to-one relationships. It describes not just romantic relationships but also business partnerships, friendships, and open enemies — anyone with whom you enter into a committed, public relationship.
In traditional astrology, the Seventh House is called the House of Marriage. It describes the quality of your partnerships, the kind of person you attract (and are attracted to), and the lessons you learn through relationship.
A planet in the Seventh House describes how you approach partnership. Venus in the Seventh House gives a natural gift for relationship, an appreciation for harmony and beauty in partnership. Mars in the Seventh House often indicates conflict in relationships, or a partner who is assertive, argumentative, or physically active. Saturn in the Seventh House may indicate delays in marriage, or a partner who is older, more serious, or more burdened.
The Seventh House is naturally associated with Libra and Venus: the sign of relationship and the planet of attraction. When planets are placed in the Seventh House, they take on something of this Libran quality, becoming more relational, more diplomatic, more focused on the other.